Compare the ages of Modric and Cross, and you can imagine how many more seasons Cross can play in Real Madrid if he wants. Last season, Real Madrid did not have Bellingham, and in the new transfer window, Real Madrid can sign a contract with another talented player, this is not a problem when the club has money. Modric is technically a very talented player, this is what allows him to play at such a high level despite his age, but he will not be able to play at this level for a long time.
If he wants to continue his playing career, he will probably have such an opportunity in other championships, but I think that he will simply end his career and rest for a while. I suspect he doesn't want to go to Saudi Arabia for the money.
Both players still got an important role to play in the teams success this season they might not be young enough to start in every match but atleast they could still be played in some important matches and deliver good performance or even serve as a role model to younger ones in the playing ground and I'll really love it if they retire in the team and become legend based on how successful they've been in the club.
Going to Saudi Arabia for money is not a bad idea also cause it would serve as a retirement funds for him and he'll also contribute to the success of any team he goes over there, however Kross still got more years to still stay at Realmadrid and enjoy football with the new rising stars in the team.